This invention relates generally to a floating magnetic head used in an external memory apparatus and more particularly to a floating magnetic head suitable for high density recording and reproduction.
Examples of the conventional floating magnetic heads used in a magnetic disk device are shown in FIGS. 13a, 13b, 14a and 14b. FIGS. 13a and 14a are perspective views of the floating magnetic heads and FIGS. 13b and 14b are enlarged view of the principal portion of the cores of the magnetic heads, respectively.
FIG. 13a shows the floating magnetic head which has been put into practical application (and is referred to as a "composite head") 10. This floating magnetic head 10 consists of a floating member 11 made of a non-magnetic material and a magnetic head core 12 made of a high permeability ferrite. In the magnetic head core 12, reference numeral 14 represents a coil and 15 does a transducing gap.
In this floating magnetic head, the floating member 11 and the magnetic head core 12 are fabricated separately, a channel 23 is formed at the end portion of an air bearing rail 13 of the floating member 11 and the magnetic head core 12 is fitted into this channel and secured thereto by a resin or glass.
Next, FIG. 14a is a perspective view of another conventional floating megnetic head 25 which is described in Japanese Patent Laid-Open No. 80519/1986.
This floating magnetic head 25 consists of a pair of magnetic core halves 16, 17, a transducing gap 18, a coil 19, and the like. The floating magnetic head 25 is fabricated by butting and joining one of the magnetic core halves 16 to the other 17 through a non-magnetic member that forms the transducing gap 18. Incidentally, the magnetic core half 17 has a structure wherein it is used also as the floating member. In the magnetic core half 16, a magnetic member 20 is interposed by a pair of narrow supporting plates 21a, 21b made of a non-magnetic member. The magnetic member 20 is made of a soft magnetic material such as an Fe-Al-Si alloy, permalloy or an amorphous alloy, and is formed on at least one of the supporting plates 21a, 21b by thin film formation technique. In the magnetic core half 16, the supporting plate 21a on which the magnetic film is formed is bonded to the other 21b by use of low melting glass.
The other magnetic core half 17 has a soft magnetic member 20' which is the same material as that of the magnetic member 20, interposed by floating members 22a and 22b and bonded by low melting glass.
In the manner described above, the magnetic core halves 16 and 17 are bonded and integrated with each other through the non-magnetic gap material and constitute the floating magnetic head 25.
In this floating magnetic head, the magnetic material that forms the magnetic circuit is the Fe-Al-Si alloy, permalloy or amorphous magnetic material and is therefore suitable as the head for high density recording.
The problems of the conventional floating magnetic heads described above will now be explained with reference to FIGS. 13b and 14b.
First of all, in the prior art example shown in FIG. 13b, the magnetic head core 12 is fitted into the channel 23 that is formed on the air bearing rail 13 of the floating member 11, and is then secured thereto by glass or the like. Accordingly, this head involves the following problems:
(1) In the steps of forming separately the magnetic core 12 and fitting and securing it into the channel 23 of the floating member 11, a position error of the magnetic head core occurs and results in the drop of production yield.
(2) Since the gap depth of the magnetic head core 12 is positioned inside the floating member 11, a reference level must be disposed separately at the time of working the gap depth and satisfactory machining accuracy cannot be obtained.
(3) Two bonding positions, at which bonding must be made by use of glass or the like, exist during the production process of the floating magnetic head. For example, the magnetic head core 12 which is bonded by use of glass when forming the transducing gap 15 is fixed by glass when it is fitted and secured to the floating member 11. When such two glass bonding portions exist, the glass used for fitting the magnetic head core to the floating member must have a lower softening point than that of the glass which is used for bonding the transducing gap of the magnetic head core, unless otherwise the glass for bonding the magnetic head core gets softened when the magnetic head core 12 is fitted to the floating member 11, and results in peel. Therefore, the glass used for bonding the magnetic head core must be the one that has a high melting point and is not softened at least the heating temperature of fitting the floating member.
For these reasons, the range of selection of glass is limited and production must be carried out within limited temperature allowance. As a result, the problems of inferior packing of glass and remaining bubbles in the glass occur.
Next, in the other floating magnetic head 25 shown in FIG. 14a, a pair of magnetic core halves 16 and 17 are coupled integrally with each other by the transducing gap 18 as shown in FIG. 14b which is an enlarged perspective view of the principal portion. In the magnetic core half 17, the magnetic member 20' constituting the magnetic circuit is interposed by the floating members 22a and 22b and is bonded to either one of the surfaces through the glass film. In FIG. 14b, for example, the magnetic member 20' is formed on the floating member 22a and the other floating member 22b is bonded onto the joint surface 24 through the glass film, thereby forming the core half 17.
In the other magnetic core half 16, the magnetic member 20 is formed on the supporting plate 21a and the other supporting plate 21b is bonded thereto through the glass film. Thereafter, the magnetic core halves 16 and 17 are coupled to each other through the transducing gap 18 to form the floating magnetic head.
The floating magnetic head having such a structure is not free from the following problems.
(1) In the floating magnetic head of this kind, a plurality of positions, where bonding must be made by glass or the like, exist in the same way as in the prior art example shown in FIGS. 13a and 13b. In other words, the floating member 22b is bonded to one (17) of the magnetic core halves after the magnetic film 20 is formed on the floating member 22a. The other magnetic core half 16 is bonded to the other supporting plate 21b after the magnetic film 20 is formed on the supporting plate 21a. Furthermore, the magnetic core halves 17 and 16 are coupled together through the transducing gap 18 to form the floating magnetic head.
If a large number of bonding positions exist, a positioning error at the time of bonding and breakage during machining will occur and reduce the production yield.
(2) If a metallic magnetic material having a high saturation flux density is used as the magnetic material, peel will occur during machining because bonding power is low between the metal and glass.
The following references are cited to show the state of the art:
(1) U.S. Patent Specification No. 3,823,416 to Warner PA1 (2) Japanese Patent Laid-Open No. 139118/1984